<!DOCTYPE html>
<html>
  <body>
    <div class="outer">
      <div class="left"></div>
      <div class="center"></div>
      <div class="right"></div>
      <style type="text/css">
        .outer {
          display: flex;
          flex-direction: row;
        }
        .left {
          border: 3px solid red;
          width: 30%;
          height: 500px;
        }
        .right {
          border: 3px solid yellow;
          width: 30%;
          height: 500px;
        }
        .center {
          border: 3px solid black;
          height: 500px;
          width: 30%;
        }
      </style>
    </div>
  </body>
</html>
